Verification of direct brachytherapy dosimetry for a single seed implant

A new technique using direct post-implant dosimetry, which does not depend explicitly on brachytherapy seed orientation or position, was explored for a prostate and a breast case. This technique, proposed by E Sajo and ML Williams (SW), uses trace amounts of positron emitters placed in the seed capsule and uses the positron emission tomography image in conjunction with a computed tomography image (PET-CT) to compute the therapeutic dose distribution in the patient. The SW technique could reduce errors in the post-implant dose computations associated with seed localization, seed shadowing and medium heterogeneity. Dose point kernels were obtained using Monte Carlo simulation for a single seed in a breast and prostate geometry. Green’s functions were computed for the positron marker and therapeutic photons using Monte Carlo (MC) simulations. Various dose computation options in the MC code MCNP were compared and the best were selected for this project. A single seed was imaged for a prostate phantom and a breast phantom using a PET-CT. The image data was used to obtain dose for the annihilation photons for the experimental seeds. The Sajo-Williams mathematical method was used to compute the therapeutic dose of the seed based on the positron marker dose. The therapeutic dose computed this way was compared to the dose obtained using the Pinnacle3 treatment planning software and to an MCNP benchmark model. For the breast case the comparison showed a good agreement with Pinnacle3, but both under-predicted the dose close to the source with respect to the benchmark. For the prostate case Pinnacle3 somewhat under-predicted the values in the MCNP benchmark, and the SW method appreciably under-predicted the dose near the source. In all cases, farther away from the source where most of the dosimetric interests lie, the agreement is very good

Mathematical Models Used for Brachytherapy Treatment Planning Dose Calculation Algorithms

Brachytherapy treatment is primarily used for the certain handling kinds of cancerous tumors. Using radionuclides for the study of tumors has been studied for a very long time, but the introduction of mathematical models or radiobiological models has made treatment planning easy. Using mathematical models helps to compute the survival probabilities of irradiated tissues and cancer cells. With the expansion of using HDR-High dose rate Brachytherapy and LDR-low dose rate Brachytherapy for the treatment of cancer, it requires fractionated does treatment plan to irradiate the tumor. In this paper, authors have discussed dose calculation algorithms that are used in Brachytherapy treatment planning. Precise and less time-consuming calculations using 3D dose distribution for the patient is one of the important necessities in modern radiation oncology. For this it is required to have accurate algorithms which help in TPS. There are certain limitations with the algorithm which are used for calculating the dose. This work is done to evaluate the correctness of five algorithms that are presently employed for treatment planning, including pencil beam convolution (PBC), superposition (SP), anisotropic analytical algorithm (AAA), Monte Carlo (MC), Clarkson Method, Fast Fourier Transform, Convolution method. The algorithms used in radiotherapy treatment planning are categorized as correction‐based and model‐based

Experimental method development for direct dosimetry of permanent interstitial prostate brachytherapy implants

Purpose: To ascertain if PET image data of a positron tracer can be used for the quantitative description of dose distribution in support of direct prostate seed dosimetry. Materials and Methods: Simulated brachytherapy seeds were constructed containing trace amounts of a positron emitter, F-18, such that all annihilation events took place in the encapsulation wall. An acrylic prostate phantom containing these seeds was imaged with a GE Discovery ST PET/CT scanner in 2D and 3D acquisition modes and several image reconstruction methods. The PET scan data was used as the input for Monte Carlo calculation of dose distribution due to the F-18. This dose distribution was then compared to computations wherein the source was restricted to the encapsulation wall. This was done to determine if the measured data could be used to accurately compute the annihilation dose, which in turn would be used to compute the therapeutic dose due to known seed activity. Results: Examination of the dose distributions indicates a close agreement between the measured data and theoretical calculations for certain cases. We found that 2D acquisition with OSEM reconstruction resulted in a maximum difference in transaxial dose distribution of 15% in a single voxel, and a mean difference of 4% for the remaining voxels. However, the mean discrepancy between dose computations based on the ideal source versus PET based source is within or close to the Monte Carlo error of 2% to 4%. These results do not reflect any optimized acquisition protocol that may further reduce the observed differences. Conclusions: This work indicates there is potential for using PET data for the proposed link between the therapeutic brachytherapy dose and the dose due to a trace amount of encapsulated positron emitter, as developed by Sajo and Williams. Because this method does not require explicit information on seed locations, clinical implementation of this technique could significantly reduce the time needed for post-implant evaluation, and several of the uncertainties and limitations inherent in current prostate brachytherapy dosimetry

Development and evaluation of low-dose rate radioactive gold nanoparticles for application in nanobrachytherapy

Depuis les dix dernières années, l’innovation des traitements d’oncologie a fait une utilisation croissante de la nanotechnologie. De nouveaux traitements à base de nanoparticules (NPs) sont notamment rendus au stade de l’essai clinique. Possédant des caractéristiques physico-chimiques particulières, les NPs peuvent être utilisées afin de bonifier l’effet thérapeutique des traitements actuels. Par exemple, l’amélioration de la curiethérapie (c.-à-d. radiothérapie interne) nécessite le développement de nouvelles procédures permettant de diminuer la taille des implants, et ce, tout en augmentant l’homogénéité de la dose déposée dans les tumeurs. Des études théoriques et expérimentales ont démontré que l’injection de NPs d’or à proximité des implants traditionnels de curiethérapie de faible débit de dose (par ex. 125I, 103Pd) permettrait d’augmenter significativement leur efficacité thérapeutique. L'interaction entre l’or et les photons émis par les implants de curiethérapie (c.-à-d. l’effet de radiosensibilisation) génère des rayonnements divers (photoélectrons, électrons Auger, rayons X caractéristiques) qui augmentent significativement la dose administrée. Dans le cadre de cette thèse, l’approche proposée était de développer des NPs d’or radioactives comme nouveau traitement de curiethérapie contre le cancer de la prostate. L’aspect novateur et unique était de synthétiser une particule coeurcoquille (Pd@Au) en utilisant l’isotope actuellement employé en curiethérapie de la prostate: le palladium-103 (103Pd, 20 keV). Dans ce cas-ci, la présence d’atomes d’or permet de produire l’effet de radiosensibilisation et d’augmenter la dose déposée. La preuve de concept a été démontrée par la synthèse et la caractérisation des NPs 103Pd@Au-PEG NPs. Ensuite, une étude longitudinale in vivo impliquant l’injection des NPs dans un modèle xénogreffe de tumeurs de la prostate chez la souris a été effectuée. L’efficacité thérapeutique induite par les NPs a été démontrée par le retard de la croissance tumorale des souris injectées par rapport aux souris non injectées (contrôles). Enfin, une étude de cartographie de la dose générée par les NPs à l’échelle cellulaire et tumorale a permis de comprendre davantage les mécanismes thérapeutiques liés aux NPs radioactives. En résumé, l’ensemble des travaux présentés dans cette thèse font office de précurseurs relativement au domaine de la nanocuriethérapie, et pourraient ouvrir la voie à une nouvelle génération de NPs pour la radiothérapie.The last decade saw the emergence of new innovative oncology treatments based on nanotechnology. New treatments using nanoparticles (NPs) are now translated to clinical trials. NPs possess unique physical and chemical properties that can be advantageously used to improve the therapeutic effect of current treatments. For instance, therapeutic efficiency enhancement related to internal radiotherapy (i.e., brachytherapy), requires the development of new procedures leading to a decrease of the implant size, while increasing the dose homogeneity and distribution in tumors. Several theoretical and experimental studies based on low-dose brachytherapy seeds (e.g., 125I and 103Pd) combined with gold nanoparticles (Au NPs) showed very promising results in terms of dose enhancement. Gold is a radiosensitizer that enhances the efficiency of radiotherapy by increasing the energy deposition in the surrounding tissues. Dose enhancement is caused by the photoelectric products (photoelectrons, Auger electrons, characteristic X-rays) that are generated after the irradiation of Au NPs. In this thesis, the proposed approach was to develop radioactive Au NPs as a new brachytherapy treatment for prostate cancer. The unique and innovative aspect of this strategy was to synthesize core-shell NPs based on the radioisotope palladium-103 (103Pd, 20 keV), which is currently used in low-dose rate prostate cancer brachytherapy. In this concept, the administrated dose is increased via the radiosensitization effect that is generated through the interactions of low-energy photons with the gold atoms. The proof-ofconcept of this approach was first demonstrated by the synthesis and characterization of the core-shell NPs (103Pd@Au-PEG NPs). Then, a longitudinal in vivo study following the injection of NPs in a prostate cancer xenograft murine model was performed. The therapeutic efficiency was confirmed by the tumor growth delay of the treated group as compared to the control group (untreated). Finally, a mapping study of the dose distribution generated by the NPs at the cellular and tumor levels provided new insights about the therapeutic mechanisms related to radioactive NPs. In summary, the studies presented in this thesis are precursors works in the field of nanobrachytherapy, and could pave the way for a new generation of NPs for radiotherapy

Deformable registration of X-ray and MRI for post-implant dosimetry in low-dose-rate prostate brachytherapy

Purpose Dosimetric assessment following permanent prostate brachytherapy (PPB) commonly involves seed localization using CT and prostate delineation using coregistered MRI. However, pelvic CT leads to additional imaging dose and requires significant resources to acquire and process both CT and MRI. In this study, we propose an automatic postimplant dosimetry approach that retains MRI for soft‐tissue contouring, but eliminates the need for CT and reduces imaging dose while overcoming the inconsistent appearance of seeds on MRI with three projection x rays acquired using a mobile C‐arm. Methods Implanted seeds are reconstructed using x rays by solving a combinatorial optimization problem and deformably registered to MRI. Candidate seeds are located in MR images using local hypointensity identification. X ray‐based seeds are registered to these candidate seeds in three steps: (a) rigid registration using a stochastic evolutionary optimizer, (b) affine registration using an iterative closest point optimizer, and (c) deformable registration using a local feature point search and nonrigid coherent point drift. The algorithm was evaluated using 20 PPB patients with x rays acquired immediately postimplant and T2‐weighted MR images acquired the next day at 1.5 T with mean 0.8 × 0.8 × 3.0 mmurn:x-wiley:00942405:media:mp13667:mp13667-math-0001 voxel dimensions. Target registration error (TRE) was computed based on the distance from algorithm results to manually identified seed locations using coregistered CT acquired the same day as the MRI. Dosimetric accuracy was determined by comparing prostate D90 determined using the algorithm and the ground truth CT‐based seed locations. Results The mean ± standard deviation TREs across 20 patients including 1774 seeds were 2.23 ± 0.52 mm (rigid), 1.99 ± 0.49 mm (rigid + affine), and 1.76 ± 0.43 mm (rigid + affine + deformable). The corresponding mean ± standard deviation D90 errors were 5.8 ± 4.8%, 3.4 ± 3.4%, and 2.3 ± 1.9%, respectively. The mean computation time of the registration algorithm was 6.1 s. Conclusion The registration algorithm accuracy and computation time are sufficient for clinical PPB postimplant dosimetry

3D BrachyView System

Prostate cancer is quickly becoming the most common form of cancer across the globe, and is commonly treated with low dose rate brachytherapy due to its curative measures and highly conformal dose delivery. It is important to ensure there is a means of real time monitoring of the dose and seed placements when radioactive seeds are implanted in the prostate gland during a low dose rate brachytherapy treatment. The BrachyView system presents as a unique system that provides the capability of 3D seed reconstruction within an intraoperative setting. In this thesis the BrachyView system is tested for its suitability, accuracy and the system is further developed so that its application in real-time intraoperative dosime-try can become a reality. The system was tested with a clinically relevant number of seeds, 98, where previously the system had only been tested with a maximum number of 30 seeds. The BrachyView system was able to reconstruct 91.8% of implanted seeds from the 98 seed dataset with an average overall discrepancy of 3.65 mm without the application of the baseline subtraction algorithm, however with its application to the data the detection efficiency was improved to 100% and an overall positional accuracy of 11.5%, correlating to a reduced overall discrepancy of 3.23 mm, was noted. It was found that with seed numbers of 30 or lower that the addition of a background subtrac-tion algorithm was not necessary, whereas for datasets containing a clinically relevant number of seeds the application of a background subtraction algorithm was paramount to reducing the noise, scatter and means for identification of newly implanted seeds that may be masked by those seed previously implanted

Anniversary Paper: A sampling of novel technologies and the role of medical physicists in radiation oncology

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135037/1/mp1006.pd

Endorectal Digital Prostate Tomosynthesis

Several areas of prostate cancer (PCa) management, such as imaging permanent brachytherapy implants or small, aggressive lesions, benefit from high image resolution. Current PCa imaging methods can have inadequate resolution for imaging these areas. Endorectal digital prostate tomosynthesis (endoDPT), an imaging method that combines an external x-ray source and an endorectal x-ray sensor, can produce three-dimensional images of the prostate region that have high image resolution compared to typical methods. This high resolution may improve PCa management and increase positive outcomes in affected men. This dissertation presents the initial development of endoDPT, including system design, image quality assessment, and examples of possible applications to prostate imaging. Experiments using computational phantoms, physical phantoms, and canine prostate specimens were conducted. Initial system design was performed computationally and three methods of endoDPT image reconstruction were developed: shift and add (SAA), backprojection (BP), and filtered BP (FBP). A physical system was developed using an XDR intraoral x-ray sensor and a GE radiography unit. The resolution and radiation dose of endoDPT were measured and compared to a GE CT scanner. Canine prostate specimens that approximated clinical cases of PCa management were imaged and compared using endoDPT, the above CT scanner, and a GE MRI scanner. This study found that the resolution of endoDPT was significantly higher than CT. The radiation dose of endoDPT was significantly lower than CT in the regions of the phantom that were not in the endoDPT field of view (FoV). Inside the endoDPT FoV, the radiation dose ranged from significantly less than to significantly greater than CT. The endoDPT images of the canine prostate specimens demonstrated qualitative improvements in resolution compared to CT and MRI, but endoDPT had difficulty in visualizing larger structures, such as the prostate border. Overall, this study has demonstrated endoDPT has high image resolution compared to typical methods of PCa imaging. Future work will be focused on development of a prototype system that improves scanning efficiency that can be used to optimize endoDPT and perform pre-clinical studies

GATE : a simulation toolkit for PET and SPECT

Monte Carlo simulation is an essential tool in emission tomography that can assist in the design of new medical imaging devices, the optimization of acquisition protocols, and the development or assessment of image reconstruction algorithms and correction techniques. GATE, the Geant4 Application for Tomographic Emission, encapsulates the Geant4 libraries to achieve a modular, versatile, scripted simulation toolkit adapted to the field of nuclear medicine. In particular, GATE allows the description of time-dependent phenomena such as source or detector movement, and source decay kinetics. This feature makes it possible to simulate time curves under realistic acquisition conditions and to test dynamic reconstruction algorithms. A public release of GATE licensed under the GNU Lesser General Public License can be downloaded at the address http://www-lphe.epfl.ch/GATE/